No, it's great that you are starting to think about college and career at your age. Most students DO wait until their senior year and that's way too late! A few things to think about:
You will be taking the PSAT soon. You should take any tutorials your school offers to do as well as you can--the PSAT is predictive of ability on the SAT. If you test well, you will do well on the MCAT, which is what you take in your junior-senior year of college before you apply to medical school. In other words, you would start in your junior year with your serious college preparation, and your high school counselor will be helping you with information about colleges, financial aid, and other matters. Your parent(s) should also be involved, as you need to know the type of school you will be able to attend--local public university, private school, etc.
Classes: Medical school is all about Chemistry--you should take as many chem classes as your school offers, and also Biology, Microbiology, and even Physics. Math is important as well since you will need to focus in science. Don't panic, just take it slowly and worry about one year at a time.
Also, you might want to think of volunteer work or extra-curricular activities such as volunteering in a hospital, at a homeless shelter, or some other area where you are helping people. That helps on your college applications and for scholarships, and it shows that you are committed to the field you have chosen.
Good grades are needed for most colleges, and then again for medical school. If you don't do well in your freshman year, you have three more years to raise your GPA. It is more important to show higher grades in the junior and senior years; some schools only consider your last two years.
At this point I wouldn't worry about what KIND of doctor you want to be--many don't even know when they enter medical school! It's important to check out different types of career paths, and you may even decide to stay in the healthcare field and do something other than be a doctor--that's OK too.
You have a clean slate for your life, you sound like and interesting and interested person, and I wish you well in high school!